From mboxrd@z Thu Jan 1 00:00:00 1970 From: Willem de Bruijn Subject: [PATCH net] packet: in packet_snd start writing at link layer allocation Date: Fri, 11 May 2018 13:24:25 -0400 Message-ID: <20180511172425.213901-1-willemdebruijn.kernel@gmail.com> Cc: davem@davemloft.net, eric.dumazet@gmail.com, Willem de Bruijn To: netdev@vger.kernel.org Return-path: Received: from mail-qk0-f194.google.com ([209.85.220.194]:35669 "EHLO mail-qk0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751378AbeEKRY3 (ORCPT ); Fri, 11 May 2018 13:24:29 -0400 Received: by mail-qk0-f194.google.com with SMTP id c137-v6so4960595qkg.2 for ; Fri, 11 May 2018 10:24:28 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: From: Willem de Bruijn Packet sockets allow construction of packets shorter than dev->hard_header_len to accommodate protocols with variable length link layer headers. These packets are padded to dev->hard_header_len, because some device drivers interpret that as a minimum packet size. packet_snd reserves dev->hard_header_len bytes on allocation. SOCK_DGRAM sockets call skb_push in dev_hard_header() to ensure that link layer headers are stored in the reserved range. SOCK_RAW sockets do the same in tpacket_snd, but not in packet_snd. Syzbot was able to send a zero byte packet to a device with massive 116B link layer header, causing padding to cross over into skb_shinfo. Fix this by writing from the start of the llheader reserved range also in the case of packet_snd/SOCK_RAW. Update skb_set_network_header to the new offset. This also corrects it for SOCK_DGRAM, where it incorrectly double counted reserve due to the skb_push in dev_hard_header. Fixes: 9ed988cd5915 ("packet: validate variable length ll headers") Reported-by: syzbot+71d74a5406d02057d559@syzkaller.appspotmail.com Signed-off-by: Willem de Bruijn --- net/packet/af_packet.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 01f3515cada0d..e9422fe451793 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -2903,13 +2903,15 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len) if (skb == NULL) goto out_unlock; - skb_set_network_header(skb, reserve); + skb_reset_network_header(skb); err = -EINVAL; if (sock->type == SOCK_DGRAM) { offset = dev_hard_header(skb, dev, ntohs(proto), addr, NULL, len); if (unlikely(offset < 0)) goto out_free; + } else if (reserve) { + skb_push(skb, reserve); } /* Returns -EFAULT on error */ -- 2.17.0.441.gb46fe60e1d-goog